On the Periodical Changes of Brightness of Two Fixed Stars. By Edward Pigott, Esq. Communicated by Sir Henry C. Englefield, Bart. F. R. S.

STOP

Early Journal Content on JSTOR, Free to Anyone in the World

This article is one of nearly 500,000 scholarly works digitized and made freely available to everyone in
the world byJSTOR.

Known as the Early Journal Content, this set of works include research articles, news, letters, and other
writings published in more than 200 of the oldest leading academic journals. The works date from the
mid-seventeenth to the early twentieth centuries.

We encourage people to read and share the Early Journal Content openly and to tell others that this
resource exists. People may post this content online or redistribute in any way for non-commercial
purposes.

Read more about Early Journal Content at http://about.istor.org/participate-istor/individuals/early-
journal-content .

JSTOR is a digital library of academic journals, books, and primary source objects. JSTOR helps people
discover, use, and build upon a wide range of content through a powerful research and teaching
platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not-for-profit
organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please
contact support@jstor.org.

Yl. On the periodiccd Changes of Brightness of two fixed Stars.
jBjv Edward Pigott, Esq. Communicated by (Sir Henry C.
Englefield, Bar^. F.R.S.

Read January 12, 1797.

Bath, August, 1796.

xtLlthough those far distant suns, the fixed stars, have baffled
all investigation with regard to our knowledge of their dis-
tance, magnitudes, and attractions ; we have, nevertheless, by
determining their periodical changes of light, established a
strong affinity between them and our sun ; and among such
an inconceivable number, we may expect to find some with
periods of rotation much longer and shorter than those we are
already acquainted with, and with changes perhaps even suf-
ficiently rapid to afford a ready means for determining accu-
rately differences of terrestrial longitudes. This would be a
most satisfactory, useful, and profitable discovery, and may be
the lot of those who have but a slight knowledge of astronomy,
provided that with great exactness, and a good memory, a con-
stant look out be given. The discoveries v/hich at present I
have the honour of laying before the Society, are the periodical
changes of brightness of two stars, one in Sobieski's Shield,
the other in the Northern Crown.

The constellation'of Sobieski's Shield consists of a very few
stars, and was formed by Hevelius, in honour of a king of Po-
land ; the variable star that now appears in it was, doubtless,
not noticed by him, as he has set down stars near it>^ which
are by times much less conspicuous. It has nearly the same
right ascension as the star /, and is about one degree more

134< Mr. PiGoTT on the periodical Changes of

south : this, for the present, suffices to point out its place ; for
as I wish to proceed immediately to ther resute, I sl^ll, for
greater perspicuity, collect at the end of this account, a more
exact determination of its right ascension and declination, as
also a plan of the stars situated near it.

When at its full and least brightness, it attains in different
periods, different degrees of brightness : I have never yet seen it
of a greater magnitude than of the 5th, nor when at its least, less
than the 7.8th. It completes all its changes in about 6g days,
being 1 4,=^ at its full brightness, without any perceptible change ;
9=+= at its least, also without any perceptible change ; 28=t= days
decreasing from the middle of its full brightness to the middle
of its least ; and 35 =i= increasing from the middle of its least
brightness to the middle of its full. These results being de-
duced from only the few observations I have made; cannot, of
course, be very accurate, but may easily and soon be corrected
by comparing any future observation with those communicated
in this paper; not relying much on the estimated magnitudes,
but principally on its comparative brightness with the stars
there mentioned and marked in the plan, the magnitudes of
which, by a mean of several observations, I have settled thus :

Magnitudes.
^ 3

' 4
m 4

/ 4-S
o 4.5

* 5
n 5
b 5.6

g 5-6

* above I 6
P 6.7
neb. 6.7
r 7
T 8

j_ The nine first letters are according to FtAMSTED, the others as
affixed by me.

the Brightness of two fixed Stars.

135

Extract from my Journal of the Observations on the Variable
in Sobie ski's Shield; made at Bath.

Dates.

Magmt

1795. Sept. 25

5

Oct. between i & 8

s

26

s

30

6

Nxjvemb, 6 & 7

6

14

5

27

5

Decemb. 14

5

1796. Feb. 12. & 13

6

March 4

7

12

6

April 7, 17, 19

5

. 30

7

May 4, 10, 12, 13

7.8

1^

-7

19

6

24

6-5

3'

5.6

June 4

5

g, 10

5

14

S

15, 20, 24

S

2S

s

29

■ 5

July 7, 8

5

16

S

19

5.6

26, 27

S

August 4, 7

5-^

12, 15

5-^

19, 21,22

S.6

,27

S.6

29

6.5

Sept. 4, 5

6

7

6

8

6.5

16

5

brighter than ^, and less than/; it has lately becRs increasing.

ditto ditto,

rather less than A ; much. brighter than P.
much less than k, and rather brighter than P.
much less than k, and rather brighter than P.
almost equal to k, and much brighter than P.
I think rather less than /^.

I could not determine which was brightest, the variable, or k.
considerably less than ^, and rather brighter than P.
much less than P.

rather brighter than P ; considerably less than Tt.
considerably brighter than P, and rather less than h
less than P ; brighter than r.

' much less than P, and rather less than r. The observation of the
_ i2th seems to express most decidedly its being less than r.
equal, or rather brighter than r ; much less than P.
ra/i6^r brighter than P.
brighter than P ; much less than k.
much brighter than P 3 rather less than i.
not quite so bright as A.

rather brighter than k ; considerably less than I.
brighter than k ; mucb less than I.

ditto, ditto, ditto,

rather brighter than k.

if any difference, brighter than k ; decreased,
equal to k.

rather less than k; considerably brighter than P ; D near its full,
less than A; rhUch brighter than P. ditto.

rather less than k; considerably brighter than P.
less than k ; much brighter than P.

ditto ditto ; moon near them.

\ between the brightness of k and p.

ditto ditto, or less bright,

much less than k; rather brighter than P.
considerably less than k\ rather brighter than P.

ditto ditto ditto ; I think it rather increased,

less than k ; brighter than P.
rather less than A 5 considerably brighter than P.

igS Mr. PiGOTT on the periodical Changes of

From these observations the periodical changes were de-
duced as follows :

The length of a single period being first settled of 67 days,
from a succession of observations between March and May,
and of 69 between April and June, we may proceed to obtain
a greater exactness from distant dates, thus :

Middle of its greatest brightness. days.

1795. Oct. 1st. 1 Interval of four periods, making the

J length of a single one - - 63J:
"[Interval of three periods, making the
10 J length of a single one - - - 64,

Middle of its least brightness.
6 "[Interval of three periods, making the
J length of a single one - - 62
"[Interval of two periods, making the
J length of a single one ^- - 59|-

A single period, on a mean - - 62 f

Had it been requisite to have given any preference to one of
these four results, I should have chosen the third ; not only on
account of the exactness of the observations themselves, but
particularly because the changes when near its least bright-
ness are quicker; however, they all agree more satisfactorily
than I think could be expected; still it rtiiist be remembered,
that the mean period here determined is merely for this set of
observations, it being yet unknown what kind of irregularities
it is liable to; for while I am now writing, in the month of
August, its changes seem difFerent from those of the four pre-
ceding periods ; and how these perturbations will terminate.

1796.

June 18

1795-

Oct. 1

1796.

April 10

-^795-

Nov. 6

1796.

May 10

-^795-

Nov. 6

1796.

March 4,

the Brightness of two fixed Stars.

•^27

cannot be settled in the present account, as I mean here to
conclude it ; but will add in the Journal, observations of as
late a date as possible.

The mean right ascensions of the stars here given, were de-
duced from observations made in the meridian with a small
transit instrument, and are, I believe, accurate. The declina-
tions are not settled with greater precision than to two or three
minutes ; and although quite sufficient to prevent any mistake,
I have, for the satisfaction of those who wish to make further
observations on them, drawn up the annexed plan, in which all
the stars they were compared to, can easilybe found; no greater-
exactness is intended. (See Tab. II.)

Mean right ascension. Declination

Computed for June 25th, 1796.
The little star T in my plan, in Sobieski's shield
The variable in Sobieski's shield - - .

Computed for June 1st, 1796.
The little star of my plan in the Northern crown
The variable in the Northern crown

The other Variable that I have discovered is, as already men-
tioned, in the Northern Crown. Its right ascension and de-
clination have just been given, as likewise the plan of the stars
near it. This star, although not in Flamstead's catalogue, is
marked on Bayer's maps of the 6th magnitude. Several
years ago, in 1783, 1784,, and 1785, I suspected it to be
changeable, which induced me to make the memorandums
here copied in the Journal, since which time I have often seen
it, but not perceiving any alteration, the dates were neglected
until the spring of 1795 ; I then had the satisfaction of finding
my suspicions confirmed, it being invisible; but on the 20th of
June, it appeared of the 9.10th magnitude, and went through

MDCCXCVU. T

In Time.
h 1 II

18 36 16,7:

t8 36 38.5

inDegrees,&c.
1 II

279 4 lo:
279 9 37

'

6 7|S
5 56 S

15 39 20,6

IS 40 11,4

234 SO 9
23s 2 51

29 8 N
28 49| N

138 Mr. PiGOTT on the periodical Changes of

its various changes as follows : in six weeks it had increased to
its full brightness, the middle time of which was August 11th,
1795. At its full brightness it was of the 6.7th magnitude, and
remained the same without any perceptible alteration for about
three weeks : it then was three weeks and a half in decreasing
to the 9.10th magnitude^ and disappeared a few days after.
Having re;appeared in the following April, 1796, it was on the
7th of May again of the 9.10th magnitude, and increasing
nearly in a similar manner as on the 20th of June the pre-
ceding year ; which completes all its changes, and gives a pe-
riod of ten months and a half.

Very remarkable and perplexing it was, that just after I had
made out the periods of these two variable stars, their changes
should appear different from those before observed; the par-
ticulars concerning that in Sobieski's Shield have been noticed:
as for this in the Northern Crown, it shews at present (being
the computed time of its full brightness), great unsteadiness,
more so, I think, than any of the variables whose periods have
been settled with certainty ; for having increased as before,
with tolerable regularity, till it attained the 7.8th magnitude, it
then kept wavering between those magnitudes, and is still so
at the present time (August) that I am closing my account of
it. I nevertheless hope to add a few more remarks in the Jour-
nal, as I have done for the other variable. Future observations
will determine how far the period of ten months and a half is
rightly settled. I am greatly inclined to think it the true one,
as the star went through all its changes progressively and
steadily. Many of the variables are occasionally liable to un-
expected changes, particularly at the attainment of their full
brightness in different periods ; such perturbed periods may

the Brightness of two fixed Stars.

13S>

perhaps be found to return after a certain number of more re-
gular ones ; but to ascertain this, requires probably a long
series of observations. The magnitude of the stars in the
Northern Crown, marked on my plan, and to some of which
the variable was compared, are here accurately fixed by a mean
of many observations. (See Tab, II.)

Magnitudes.
a. 2.3

4-3

j^AII these characters are according to Bayer, except the foul? last, which
'^ I have added.

'.)<

6

ir 6.7
W 7
8.9

P 9

X 10

J

I have in this paper followed, as much as possible, the same
method and deductions as in my others, which the Society^have
done me the honour of publishing.* The subject of them all
being very similar, it was difficult to avoid sometimes repeat-
ing the same remarks, which, if omitted, might perhaps occa-
sion some uncertainty, and perplex those who do not recollect
or have not read the former papers. I shall now conclude with
■my observations on the variable in the Crown,

• See Pbil. Trans. Vol. 75, and 76, &c.

Te

14,0

Mr. PiooTT on the periodical Changes of

Extracts from my Journal, of the Observations on the Variable
in the Northern Crown ; made at Bath.

Dates.

1783. July 27

30

August 8

1784. July II

1785.
1 795'

May
May
June

July

August

Sept.

»79$.

Nov.
Dec.
Jan.
Feb.
March 27
28
April

14
20
28
20

23

29

6

7
13
24 1

3U

2

6
It

17

21

28

t.
13

IS

16

20
22 .

I
12
II
12

May

17/

10 I
12 J
'9 ,

iMagnit.
7.8

7
7
7

6.7

6.7

9.10

9
8.9

6-7

6.7

7.6

7
8.7

9

9.10

10
9.10

9

8.9

seen with difficulty with an opera-glass. r^ as, in these four observa-

much brighter. I tions.it wasnotcom-

thoughtheairwasha-zy.IcouldseeitT./fADo. \ ^J^iT^tTil^l
saw It distinctly— opera-glass. J on.

f thought it considerably brighter than last year.

\_ rather less than v, but evidently brighter than w.
not so bright as 5, equal to ir, and brighter than w.

t is marked less than ir, and brighter than the 7.8th magnitude
not visible with an opera-glass.

evidently less than ; rather less than P ; rather brighter than x.
equal to, or brighter than P.
evidently brighter than P j nearly equal to 0.

evidently brighter than ; nearly equal to w.

certainly brighter than w, and rather less than b- j.

nearly equal to n-; no perceptible alteration during these dates.

less than tt ; moon nearly full.

evidently less than b- ; if any difference brighter than w.

evidently less than w ; if any difference brighter than 0.
less than 0, and equal to P.
equal to, or less than P ; brighter than x.

' not visible with an excellent night-glass ; therefore less than the
ith magnitude ; a remarkably rapid disappearance ; air clear.

not visible with an opera-glass, with which I can, when the air
is very clear, see the star of my plan.

not visible with the night-glass ; therefore not of the 1 ith magnit.
visible with night-glass ; less than x.

brighter than x ; rather less than P.

less than 0, and equal to, or rather brighter than P.
equal to, or rAther brighter than 0. 5 near fulL

the Brightness of two fixed Stars.

141

Continuation of the Observations on the variable Star in the
Northern Crown. Bath.

1796.

Dates.
May

June

July

Aug.

Sept.

Magnitc

7.8

7.8

7.8

7
7
7

rather brighter than o.
brighter than ; less than w.

[

between the loth and 24th I often tried to see it with an opera-
glass, but owing to the mponand twilight, I could not, though
the VD was by times perceptible, therefore it could not be
brighter than the 7.8th magnitude.

ralber brighter than o; considerably less than w.

fduring these dates it has in general been set down much brighter
I than 0, and rather less than w, though sometimes more de-
<(' cidedly less than w ; but these very small differences are ever
I difficult to ascertain, owing to the disposition of the eye, at»
[_ mosphere, and various lights.

equal tow, no moonlight.

equal to, or rather less than w.
equal to, if not brighter than w.
equal to, if not less than w.